A motor vehicle is generally equipped with an alternator which is driven by the thermal engine of the vehicle, in order to ensure that the battery is charged, and to produce the electric energy necessary for the on-board electrical network to which the various items of equipment are connected.
The alternator is generally driven by a belt which is engaged on the drive shaft. It is thus implanted in the immediate vicinity of the thermal engine, under the engine bonnet.
Taking into account the development of the thermal engines of vehicles which are increasingly confined, the ambient temperature under the engine bonnet is increasing more and more.
An alternator is a rotary electrical machine which substantially comprises a rotor which is integral in rotation with a shaft which rotates inside a stator which is provided in a housing.
One end of the rotor shaft is provided with collector rings on which the brushes rub, guided by a brush-holder which is supported by the housing, and which rings make it possible to supply an excitation winding of the rotor from the on-board electrical network.
The stator windings produce a voltage which, after being rectified, is regulated by a voltage regulator which controls the excitation current of the rotor.
The same development of vehicles which has led to increased confinement of the thermal engines has led to the need to make the alternators more compact.
For this purpose it is known to integrate the voltage regulator device and the brush-holder in an assembly in a single piece made of electrically insulating material, which is provided on the housing, around the bearing of the rotor shaft, opposite collector rings.
In the confined environment of the engine bonnet, the temperature to which the alternator is subjected in operation can rise to 125° C.
The temperature of the brushes can reach 200° C. because of the friction with the collector rings.
Consequently, an alternator comprises a fan integral with the rotor, which aspirates the relatively cool air obtained from the exterior, in order to cool the interior of the housing.
The high temperature of the brushes causes an increase in their wear, and a decrease in the performance of the alternator.
The Korean patent application KR 20100048703, in the name of the company VALEO ELECTRICAL SYSTEMS KOREA proposes a solution to improve the cooling of one of the brushes of an alternator of a motor vehicle, by making part of the axial flow of air aspirated by the fan circulate in the interior of the brush-holder.